The use of electrodes to sense and measure bio-potential signals is widely practiced in the medical field as part of the various diagnostic tools like electrocardiography (ECG/EKG) for monitoring heart function and electroencephalography (EEG) for studying brain activity and the like. The prior art for these techniques is to use a metal electrode which is in contact with its ionic form through a gel-bound electrolyte which then contacts the skin. A commonly used system of this type is the “wet” electrode which is typically a Ag/AgCl electrode. These systems suffer from many disadvantages documented in literature such as the requirement of skin preparation including removal of hairs by shaving, and removal of the Stratum Corneum by scrubbing. Furthermore, wet electrodes commonly cause skin irritation in persons with sensitive skin.
Previous work on biopotential sensors has been done by Licata and Mitchell on the use of soft elastomeric bristles filled with a conductive liquid as a biopotential sensor (see U.S. Pat. No. 6,510,333). The technique of U.S. Pat. No. 6,510,333 art does not require preparation of the skin, however it does require liquid to be in the bristles and also recommends an abrasive scrubbing of the skin in order to eliminate resistance from the surface of the skin. The bristles also require refilling throughout their lifetime which can be an added inconvenience to the user.
Previous work on dry electrodes has been done by Dunseath Jr. (see U.S. Pat. No. 4,865,039) on a dry electrode assembly. However, the maximum allowed volume resistivity for these electrodes to be effective it reported to be 200 KΩ-cm using a graphite-loaded polyurethane foam material. Moreover, this assembly requires a lead amplifier for improving the signal strength of the bio-potentials.
Previous work on dry electrodes has also been done by Schmidt, Lisy, Skebe, and Prince from Orbital Research Inc. (U.S. Pat. No. 7,032,301) on a dry physiological recording electrode that does not require any skin preparation. This prior art assembly requires constant contact with the skin. To ensure constant contact the assembly pierces the skin in order to obtain a biopotential signal which can cause pain and discomfort to the user.